Ultraviolet excited light-emitting device

ABSTRACT

An ultraviolet excited light-emitting device is disclosed. The ultraviolet excited light-emitting device comprises a phosphor having at least one selected from the group consisting of Eu and Mn as an activator and a compound represented by a formula (1):
 
M 1 M 2 M 2   3 O 6   (1)
 
wherein M 1  is at least two selected from the group consisting of Ca, Sr and Ba, or Sr or Ba, M 2  is at least one selected from the group consisting of Mg and Zn, and M 3  is at least one selected from the group consisting of Si and Ge in the formula (1).

TECHNICAL FIELD

The present invention relates to an ultraviolet excited light-emittingdevice.

BACKGROUND ART

An ultraviolet excited light-emitting device include cold cathode tube,three wavelength type fluorescent lamps and the like, and is applied toa backlight for a liquid crystal display. An ultraviolet excitedlight-emitting device (cold cathode tube) applied to a backlightcomprises a substrate, a phosphor and an electrode.

The ultraviolet excited light-emitting device including a phosphorrepresented by CaMgSi₂O₆:Eu is known, however, in viewpoint of enhancingbrightness of liquid crystal display, ultraviolet excited light-emittingdevice having higher brightness are desired.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide an ultraviolet excitedlight-emitting device having high brightness.

The present inventors have studied to solve the problems described aboveand then completed the present invention.

The present invention provides an ultraviolet excited light-emittingdevice comprising a phosphor including at least one selected from thegroup consisting of Eu and Mn as an activator and a compound representedby a formula (1):M¹M²M₂ ³O₆  (1)wherein M¹ is at least two selected from the group consisting of Ca, Srand Ba, or Sr or Ba, M² is at least one selected from the groupconsisting of Mg and Zn, and M³ is at least one selected from the groupconsisting of Si and Ge in the formula (1).

MODE FOR CARRYING OUT THE INVENTION

The phosphor in the ultraviolet excited light-emitting device of thepresent invention includes a compound represented by the above formula(1) and an activator.

In the formula (1), M¹ is a divalent metal element, and a combination ofCa and Sr, a combination of Ca and Ba, a combination of Sr and Ba, acombination of Ca, Sr and Ba, Sr or Ba.

In the formula (1), M² is a divalent metal element, and a combination ofMg and Zn, Mg or Zn, preferably Mg.

In the formula (1), M³ is a quaternary metal element, and a combinationof Si and Ge, Si or Ge, preferably Si.

The activator is a combination of Eu and Mn, Eu or Mn, preferably Eu.

The phosphor is preferably a compound represented by the followingformula (2) including Eu as an activator, more preferably the compoundfurther satisfying a being more than 0 and not more than 0.1;(M¹ _(1-a)Eu_(a))M²M³ ₂O₆  (2)wherein, in the formula (2), each of M¹, M² and M³ is same to respectiveM¹, M² and M³ in the formula (1)).

Among these compounds, a compound represented by the following formula(3) wherein M¹ is a combination of Ca and Sr, M² is Mg and M³ is Si isparticularly preferable;Ca_(1-b-c)Sr_(b)Eu_(c)MgSi₂O₆  (3)wherein, in the formula (3), b is more than 0.1, preferably not lessthan 0.2 and not more than 0.4, and c is more than 0, preferably notless than 0.003 and not more than 0.1, preferably not more than 0.05.

The phosphor in the ultraviolet excited light-emitting device of thepresent invention, in viewpoint of enhancing brightness, preferably hasthe same crystal structure as diopside.

The phosphor in the ultraviolet excited light-emitting device of thepresent invention has usually an average particle diameter of about notless than 0.5 μm and about not more than 8 μm.

The phosphor in the ultraviolet excited light-emitting device of thepresent invention may be produced by calcining a metal compound with acomposition ratio of the phosphor having a compound represented by theformula (1) and an activator. For example, at least two metal compoundsare weighed to obtain a predetermined composition, followed by mixing,and then the mixture is calcined.

The metal compounds include calcium compounds, strontium compounds,barium compounds, europium compounds, manganese compounds, magnesiumcompounds, zinc compounds, silicon compounds and germanium compounds,compounds containing these metals. Examples of the compounds includehigh purity (about 99% by weight or more of purity) hydroxides,carbonates, nitrates, halides and oxalates which can be converted to anoxide by decomposition at high temperature, or high purity (about 99% byweight or more of purity) oxides.

The metal compounds are weighed to form predetermined composition. Forexample, when producing a phosphor represented by a formula ofCa_(0.792)Sr_(0.2)Eu_(0.008)MgSi₂O₆, CaCO₃, SrCO₃, Eu₂O₃, MgO and SiO₂may be mixed in molar ratio of 0.792:0.2:0.004:1:2. When producing aphosphor represented by a formula ofCa_(0.692)Sr_(0.296)Eu_(0.012)MgSi₂O₆, CaCO₃, SrCO₃, Eu₂O₃, MgO and SiO₂may be mixed in molar ratio of 0.692:0.296:0.006:1:2.

The weighed metal compounds may be mixed, for example, by a ball mill,V-shape mixer, a vessel equipped with agitator. To enhance crystallinityof the phosphor obtained and control crystal size, the metal compoundsmay be added with appropriate amount of a flux to be mixed. Examples ofthe flux include LiF, NaF, KF, LiCl, NaCl, KCl, Li₂CO₃, Na₂CO₃, K₂CO₃,NaHCO₃, NH₄Cl, NH₄I and the like.

Calcination of the mixture is preferably carried out under a reductiveatmosphere, for example, preferably under a nitrogen (N₂) atmospherecontaining hydrogen from about 0.1% by volume to about 10% by volume orunder an argon (Ar) atmosphere containing hydrogen from about 0.1% byvolume to about 10% by volume. To gain highly reductive effect, amixture of at least two metal compounds may be added with an appropriateamount of carbon, and then the mixture may be calcined; or at least twometal compounds may be mixed with an appropriate amount of carbon, andthen the mixture may be calcined. Calcination is usually carried outunder conditions of temperature: from about 900° C. to about 1500° C.,and time: about 1 hour to about 100 hours.

When a compound which can be converted to an oxide by decomposition athigh temperature such as hydroxide, carbonate, nitrate, halide andoxalate is contained in the mixture above, the mixture may bepre-calcined before calcination. The pre-calcination may be carried outunder an oxidative atmosphere (for example, in air) or reductiveatmosphere. The pre-calcination may be carried out at a temperature toremove crystal water in hydroxide, carbonate, nitrate, halide andoxalate, or at a temperature to convert hydroxide, carbonate, nitrate,halide and oxalate to an oxide, usually carried out from about not lessthan 400° C. and about less than 900° C.

The phosphor obtained by calcination may be pulverized, washed orclassified. Pulverization may be carried out by using a ball mill or ajet mill. Thus obtained phosphor may be subjected to heat treatment. Bythe heat treatment, a phosphor having much higher brightness may beproduced. The heat treatment may be carried out under similar conditionsto the calcination. The heat treatment may be carried out twice or more.

The ultraviolet excited light-emitting device of the present inventionincludes the phosphor described above, usually includes the phosphor anda substrate. The ultraviolet excited light-emitting device preferablyincludes a substrate and a phosphor layer on the substrate. Examples ofother ultraviolet excited light-emitting device include cold cathodetubes (of a backlight for liquid crystal display), three wavelength typefluorescent lamps and the like. The ultraviolet excited light-emittingdevices usually include the phosphor described above, a red phosphor, agreen phosphor, a substrate and an electrode. The red phosphor may beexcited by ultraviolet rays to emit red light, but should not beparticularly limited thereto. The green phosphor may be excited byultraviolet rays to emit green light, but should not be not particularlylimited thereto.

The ultraviolet excited light-emitting device described above is excitedby irradiation of ultraviolet rays, preferably of a light withwavelength of more than about 200 nm and not more than about 400 nm, toemit blue light with high brightness.

A method for producing an ultraviolet excited light-emitting device isexplained with high intensity fluorescent lamp (=a lamp having highpower consumption per unit area of the lamp wall). The high intensityfluorescent lamp may, for example, be manufactured by a methodcomprising the steps of (i) to (vi):

(i) mixing the blue phosphor described above with a solvent (aqueouspolyethylene oxide solution and the like);

(ii) coating the coating solution obtained on an inner wall of asubstrate (glass tube and the like);

(iii) drying the coating film obtained, if necessary;

(iv) calcining the coating film at from 300 to 600° C.;

(v) attaching an electrode (filament and the like) on the substrate; and

(vi) exhausting the substrate, followed by enclosing a rare gas (Ar, Kr,Ne and the like) and mercury, and then capping.

EXAMPLES

The present invention is described in more detail by following Examples,which should not be construed as a limitation upon the scope of thepresent invention. Brightness of an ultraviolet excited light-emittingdevice was measured by the following method. Brightness of ultravioletexcited light-emitting element:

The measurement was carried out by irradiating ultraviolet rays of 254nm wavelength (bright line of mercury) with a mercury lamp.

REFERENCE

Calcium carbonate (manufactured by Ube Material Industries, Ltd.,CaCO₃), europium oxide (manufactured by Shin-Etsu Chemical Co., Ltd.,Eu₂O₃), magnesium carbonate (manufactured by Kyowa Chemical IndustryCo., Ltd., MgCO₃) and silicon dioxide SiO₂ (manufactured by NIPPONAEROSIL CO., LTD., SiO₂) were weighed in a manner such that the molarratio of CaCO₃:Eu₂O₃:MgCO₃:SiO₂ was 0.992:0.004:1:2, and then mixed;thereafter, the mixture was calcined under N₂ atmosphere containing H₂of 2% by volume at 1200° C. for 2 hours. The calcined material wassubjected to a heat treatment under N₂ atmosphere containing H₂ of 2% byvolume at 1200° C. for 2 hours. The heat treatment was conducted oncemore. The phosphor obtained had the same crystal structure as diopsideand included a compound represented by a formula ofCa_(0.992)Eu_(0.008)MgSi₂O₆.

The phosphor described above was put on a glass substrate to form aphosphor layer to obtain an ultraviolet excited light-emitting device.The ultraviolet excited light-emitting device emitted blue light byirradiation of ultraviolet rays. The brightness of the ultravioletexcited light-emitting device was assumed to be 100.

Example 1

Calcium carbonate (manufactured by Ube Material Industries, Ltd.,CaCO₃), strontium carbonate (manufactured by Wako Pure ChemicalIndustries, Ltd., SrCO₃), europium oxide (manufactured by Shin-EtsuChemical Co., Ltd., Eu₂O₃), magnesium carbonate (manufactured by KyowaChemical Industry Co., Ltd., MgCO₃) and silicon dioxide SiO₂(manufactured by NIPPON AEROSIL CO., LTD., SiO₂) were weighed in amanner such that the molar ratio of CaCO₃:SrCO₃:Eu₂O₃:MgCO₃:SiO₂ was0.932:0.06:0.004:1:2, and then mixed; thereafter, the mixture wascalcined under N₂ atmosphere containing H₂ of 2% by volume at 1180° C.for 2 hours. The calcined material was subjected to a heat treatmentunder N₂ atmosphere containing H₂ of 2% by volume at 1200° C. for 2hours. The heat treatment was conducted once more. The phosphor obtainedhad the same crystal structure as diopside and included a compoundrepresented by a formula of Ca_(0.932)Sr_(0.06)Eu_(0.008)MgSi₂O₆.

The phosphor described above was put on a glass substrate to form aphosphor layer to obtain an ultraviolet excited light-emitting device.The ultraviolet excited light-emitting device emitted blue light byirradiation of ultraviolet rays. The ultraviolet excited light-emittingdevice had a brightness of 136.

Example 2

Except that the molar ratio of CaCO₃:SrCO₃:EU₂O₃:MgCO₃:SiO₂ was changedto 0.792:0.2:0.004:1:2, the same operation in Example 1 was conducted.The phosphor obtained had the same crystal structure as diopside andincluded a compound represented by a formula ofCa_(0.792)Sr_(0.2)Eu_(0.008)MgSi₂O₆.

The phosphor described above was put on a glass substrate to form aphosphor layer to obtain an ultraviolet excited light-emitting device.The ultraviolet excited light-emitting device emitted blue light byirradiation of ultraviolet rays. The ultraviolet excited light-emittingdevice had a brightness of 213.

Example 3

Except that the molar ratio of CaCO₃:SrCO₃:Eu₂O₃:MgCO₃:SiO₂ was changedto 0.692:0.3:0.004:1:2, the same operation in Example 1 was conducted.The phosphor obtained had the same crystal structure as diopside andincluded a compound represented by a formula ofCa_(0.692)Sr_(0.3)Eu_(0.008)MgSi₂O₆.

The phosphor described above was put on a glass substrate to form aphosphor layer to obtain an ultraviolet excited light-emitting device.The ultraviolet excited light-emitting device emitted blue light byirradiation of ultraviolet rays. The ultraviolet excited light-emittingdevice had a brightness of 226.

Example 4

Except that the molar ratio of CaCO₃:SrCO₃:EU₂O₃:MgCO₃:SiO₂ was changedto 0.692:0.296:0.006:1:2, the same operation in Example 1 was conducted.The phosphor obtained had the same crystal structure as diopside andincluded a compound represented by a formula ofCa_(0.692)Sr_(0.296)Eu_(0.012)MgSi₂O₆.

The phosphor described above was put on a glass substrate to form aphosphor layer to obtain an ultraviolet excited light-emitting device.The ultraviolet excited light-emitting device emitted blue light byirradiation of ultraviolet rays. The ultraviolet excited light-emittingdevice had a brightness of 231.

1. An ultraviolet excited light-emitting device comprising a phosphorwhich comprises a compound represented by a formula (3);Ca_(1-b-c)Sr_(b)Eu_(c)MgSi₂O₆  (3) wherein b is more than 0.1 and notmore than 0.4 and c is more than 0 and not more than 0.1.
 2. Theultraviolet excited light-emitting device according to claim 1, whereinthe wavelength of ultraviolet is more than about 200 nm and not morethan about 400 nm.